In various applications a person is required to provide confidential information, such as a personal identification number (PIN) in automatic teller machines (ATM) and a user ID number in mobile point of sale (POS) terminals. Typically, the confidential information is provided via a man-machine interface such as a keyboard. The keyboard and its interfaces may be vulnerable to attacks in which an unauthorized party attempts to recognize the input confidential information. Examples of prior art techniques for preventing keyboard attacks are provided below.
U.S. Pat. No. 6,426,710, whose disclosure is incorporated herein by reference, describes a security keyboard matrix scanning method. The method utilizes bi-directional input/output ports (e.g., X-port and Y-port), in which each line of the X-port and the Y-port can be selectively designated as a sensing line or an output line, to construct the X-port and Y-port such that at least one line of one of the two ports can output a scanning signal representative of a dummy scanning signal at the time the actual scanning signal is output from another line of either port.
U.S. Patent Application Publication 2011/0095919, whose disclosure is incorporated herein by reference, describes a keyboard having a plurality of key fields and a plurality of capacitive elements, which are associated with the key fields, and measuring electronics. The measuring electronics are implemented for the purpose of detecting a change of the capacitance value of one of the capacitive elements between a non-actuation level, which is in a first capacitance value range, and an actuation level, which is in a second capacitance value range, and then outputting an actuation signal. An attempt to manipulate the keyboard can thus be detected on the basis of the capacitance value increase associated therewith.